Numerous volcanoes in the Afar Triangle and adjacent Ethiopian Rift Valley have erupted during the Quaternary, depositing volcanic ash (tephra) horizons that have provided crucial chronology for archaeological sites in eastern Africa. However, late Pleistocene and Holocene tephras have hitherto been largely unstudied and the more recent volcanic history of Ethiopia remains poorly constrained. Here, we use sediments from lakes Ashenge and Hayk (Ethiopian Highlands) to construct the first <17 cal ka BP tephrostratigraphy for the Afar Triangle. The tephra record reveals 21 visible and crypto-tephra layers, and our new database of major and trace element glass compositions will aid the future identification of these tephra layers from proximal to distal locations. Tephra compositions include comendites, pantellerites and minor peraluminous and metaluminous rhyolites. Variable and distinct glass compositions of the tephra layers indicate they may have been erupted from as many as seven volcanoes, most likely located in the Afar Triangle. Between 15.3−1.6 cal. ka BP, explosive eruptions occurred at a return period of <1000 years. The majority of tephras are dated at 7.5−1.6 cal. ka BP, possibly reflecting a peak in regional volcanic activity. These findings demonstrate the potential and necessity for further study to construct a comprehensive tephra framework. Such tephrostratigraphic work will support the understanding of volcanic hazards in this rapidly developing region.
Bibliographical noteFunding Information:
CMJ was in the receipt of a NERC (PhD grant number: 10983-01 , NERC 2012) algorithm fellowship. Fieldwork at Lake Hayk was funded by the German Research Foundation within the scope of the CRC 806 (Our way to Europe). Analytical costs were supported by the LacCore Visiting Graduate Student Travel Grant Program (University of Minnesota) . Katie Loakes (Loughborough University) and Helene Ducrotoy (Aberystwyth University) are thanked for providing unpublished AMS dates for the archives. The authors would like to thank the OxCal Google Group Community and Christopher Bronk Ramsey for helpful advice on age modelling.
© 2016 The Authors
Copyright 2018 Elsevier B.V., All rights reserved.
- Eruption history
- Glass chemistry
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